3장. Garbage Collection

Java Performance
artdb@ex-em.com | performeister.tistory.com | twitter @novathinker

Garbage Collection

Java Performance
2


1) Garbage Collection
2) Garbage Collection Algorithm
3) Hotspot JVM Garbage Collection

4) IBM JVM Garbage Collection

Java Performance
3
Java Performance Fundamental | twitter @novathinker
artdb@ex-em.com | performeister.tistory.com
Garbage Collection

• Garbage Collection
– Garbage Collector
– Unreferenced Memory
–
– Fragmentation

“Heap storage for objects is reclaimed by an automatic
storage management system (typically a garbage
collector); objects are never explicitly deallocated.”
- Java Virtual Machine Speculation, Section 3.5.3 [JVMS2
1999]

Java Performance
4
Garbage Collection

!
Garbage
Collector

Java Performance
4
Garbage Collection

! object
Garbage
Collector
Heap memory
.

Java Performance
4
Garbage Collection

! object
Garbage
Collector
Heap memory
.

Garbage Collection
Memory Recycling Heap
Fragmentation .

Java Performance
4
Garbage Collection

! object
Garbage
Collector
Heap memory
.

Garbage Collection
Memory Recycling Heap
Fragmentation .

• JVM heap new, newarray, anewarray, multianewarray instruction
instruction
• JVM Spec Garbage Collection Algorithm

Java Performance
5
Garbage Collection

!
Garbage
Collector

Java Performance
5
Garbage Collection

Memory

! Memory System
Garbage
Collector
crash
.

Java Performance
5
Garbage Collection

Memory

! Memory System
Garbage
Collector
crash
.

Program

CPU Time Scheduling

.

Java Performance
6
Garbage Collection

– Garbage Collection

Java Performance
7
Garbage Collection

Java Performance
7
Garbage Collection

ROOT SET

Java Performance
7
Garbage Collection

ROOT SET

Local Variable,
Operand Stack

Java Performance
7
Garbage Collection

ROOT SET

Local Variable,
Operand Stack

Class
Constant Pool
Reference

Java Performance
7
Garbage Collection

ROOT SET

Local Variable, Unreleased Native
Operand Stack Method
Object
Reference
Class
Constant Pool
Reference

Java Performance
8
Garbage Colletion

• Root Set

Java Performance
9
Garbage Colletion

• Memory Leak
class Main{
public static void main (String args[]) {
Leak lk = new Leak();
for(int a=0; a<9000000; a++) {
lk.addList(a);
lk.removeStr(a);
}
}
}

class Leak {
ArrayList lst = new ArrayList();
public void addList(int a) {
lst.add(" "+a);
}
public void removeStr(int i) {
Object obj = lst.get(i);
obj = null;
}
}

Java Performance
9
Garbage Colletion

• Memory Leak
class Main{
public static void main (String args[]) {
Leak lk = new Leak();
for(int a=0; a<9000000; a++) {
lk.addList(a);
lk.removeStr(a);
}
} Why leak?
}

class Leak {
ArrayList lst = new ArrayList();
public void addList(int a) {
lst.add(" "+a);
}
public void removeStr(int i) {
Object obj = lst.get(i);
obj = null;
}
}

Java Performance
10

Garbage Collection
Algorithm

Java Performance
11


Garbage Collection Algorithm
1) Reference Counting Algorithm
2) Mark-and-Sweep Algorithm
3) Mark-and-Compacting Algorithm
4) Copying Algorithm
5) Generational Algorithm
6) Train Algorithm
7) Adaptive Algorithm

Java Performance
12

• Garbage Collection Algorithm

Java Performance
12


Garbage Object Detection
• Live Object : Root Set
• Garbage Object

Java Performance
12


Garbage Object Detection
• Live Object : Root Set
• Garbage Object

Garbage Object
• Heap Memory Reclaim

Java Performance
13

• Reference Counting Algorithm
• Mark-and-Sweep Algorithm
• Copying Algorithm
• Mark-and-Compacting Algorithm
• Generational Algorithm
• Train Algorithm
• Adaptive Algorithm

Java Performance
14

– GC
– Object Reference count
– Reference Count 0 GC
– Object GC Object
Object Object Count
Count

Java Performance
15

Integer

RefCnt 00

Integer

RefCnt 00

Integer

RefCnt 00

Java Performance
15

Integer
Object a = new Ingeter(1);

RefCnt 00

Integer

RefCnt 00

Integer

RefCnt 00

Java Performance
15

Integer
Object a = new Ingeter(1); a 1
RefCnt 01
0

Integer

RefCnt 00

Integer

RefCnt 00

Java Performance
15

Integer
Object b = a; RefCnt 01
0

Integer

RefCnt 00

Integer

RefCnt 00

Java Performance
15

Integer
Object b = a; b RefCnt 01
0
2

Integer

RefCnt 00

Integer

RefCnt 00

Java Performance
15

Integer
0
2

Integer

Object a = new Ingeter(1); RefCnt 00

Integer

RefCnt 00

Java Performance
15

Integer
0
2

Integer

a 1
Object a = new Ingeter(1); 0
RefCnt 01
Integer

RefCnt 00

Java Performance
15

Integer
0
2

Integer

a 1
RefCnt 01
Object b = new Ingeter(2); Integer

RefCnt 00

Java Performance
15

Integer
0
2

Integer

a 1
RefCnt 01
2
b RefCnt 01
0

Java Performance
15

Integer
0
2

Integer

a 1
RefCnt 01
a = b; 2
b RefCnt 01
0

Java Performance
15

Integer
0
2

Integer

a 1
RefCnt 01
a = b; 2
b RefCnt 01
0
2

Java Performance
16

Java Performance
16

Object a = new TwoIngeter(new Integer(1), new Integer(2));

Java Performance
16


Integer
1
TwoInteger
RefCnt 00
1
ref
a
RefCnt 00
1 Integer
2
RefCnt 01
0

Java Performance
16


a = null;

Integer
1
TwoInteger
RefCnt 00
1
ref
a
RefCnt 00
1 Integer
2
RefCnt 01
0

Java Performance
16


a = null;

Integer
1
TwoInteger
RefCnt 00
1
ref
a GC
RefCnt 00
1 Integer
2
RefCnt 01
0

Java Performance
16


a = null;

Integer
1
RefCnt 00
1
a
Integer
2
RefCnt 01
0
0

Java Performance
17


• Garbage Object
• Garbage
• Garbage Collector ( )

• Reference Count
• Linked List Reference Count 0
Leak

Java Performance
18

a

Linked List
next ref
RefCnt 02

Linked List
next ref
RefCnt 11

Linked List
next ref
RefCnt 01

Java Performance
18

a

Linked List
next ref
2
RefCnt 01

Linked List
next ref
RefCnt 11

Linked List
next ref
RefCnt 01

Java Performance
19

– Root Set Reference
– Tracing Algorithm
– Mark Sweep
• Mark : Live Object Mark
(Object ﬂag or bitmap table )
• Sweep : Heap Mark

Java Performance
20

R ref ref ref
 flag  flag  flag

ref ref ref

ref ref ref

Java Performance
20

Mark Phase
R ref ref ref

ref ref ref

ref ref ref

Java Performance
20

Mark Phase
R ref ref ref

 flag 
 flag 
 flag

ref ref ref
 flag  flag 
 flag

ref ref ref
 flag 
 flag 
 flag

Java Performance
20

Sweep Phase
R ref ref ref

 flag 
 flag 
 flag

ref ref ref
 flag  flag 
 flag

ref ref ref
 flag 
 flag 
 flag

Java Performance
20

Sweep Phase
R ref ref ref

 flag 
 flag 
 flag

ref

 flag

ref ref

 flag 
 flag

Java Performance
20

R ref ref ref

 flag 
 flag 
 flag

ref

 flag

ref ref

 flag 
 flag

Java Performance
20

R ref ref ref

ref
 flag

ref ref
 flag  flag

Java Performance
21


• Reference
• Reference Overhead

• Suspend
• Fragmentation
 Memory

Java Performance
22

– Fragmentation Memory
Algorithm
– Mark Compaction
• Mark Phase : Live Object Mark
• Compaction : Live Object Memory

– Handle
• Mark Phase : Handle Marking
• Compaction : Object Handle Update

Java Performance
23

– Compaction
Arbitrary Worst

4 1 2 3
1 2 3 4

Linear

1 3 4 2

• Arbitrary : Sliding
• Linear : Pointer
1 2 3 4
• Sliding : Allocation
Best

Java Performance
24

2

Handle
0  flag
1  flag T22 A 5 Z 1
2  flag T11
3  flag T12
B 9 W 7
4  flag
5  flag T21
6  flag Q 3 C 2
7  flag T31
8  flag
9  flag T32

Java Performance
24

2 Mark Phase
Handle
0  flag
1  flag T22 A 5 Z 1
2  flag T11
3  flag T12
B 9 W 7
4  flag
5  flag T21
6  flag Q 3 C 2
7  flag T31
8  flag
9  flag T32

Java Performance
24

2 Mark Phase
Handle
0  flag
1  flag T22 A 5 Z 1

2  flag T11
3  flag T12
B 9 W 7
4  flag

5  flag T21
6  flag Q 3 C 2
7  flag T31
8  flag

9  flag T32

Java Performance
24

2 Compation Phase
Handle
0  flag
1  flag T22 A 5 Z 1

2  flag T11
3  flag T12
B 9 W 7
4  flag

5  flag T21
6  flag Q 3 C 2
7  flag T31
8  flag

9  flag T32

Java Performance
24

2 Compation Phase
Handle
0  flag
1  flag T22 A 5

2  flag T11
3  flag T12
B 9
4  flag

5  flag T21
6  flag C 2
7  flag T31
8  flag

9  flag T32

Java Performance
24

2 Compation Phase
Handle
0  flag
1  flag T22 A 5 B 9

2  flag T11
3  flag T12
4  flag

5  flag T12
T21
6  flag C 2
7  flag T31
8  flag

9  flag T32

Java Performance
24

2 Compation Phase
Handle
0  flag
1  flag T22 A 5 B 9

2  flag T11
3  flag T12
C 2
4  flag

5  flag T12
T21
6  flag
7  flag T31
8  flag

9  flag T21
T32

Java Performance
24

2

Handle
0  flag
1  flag T22 A 5 B 9
2  flag T11
3  flag T12
C 2
4  flag
5  flag T12
T21
6  flag
7  flag T31
8  flag
9  flag T21
T32

Java Performance
25


• Fragmentation
• Memory

• Reference Object Access Overhead
• Suspend

Java Performance
26

– Stop-the-Copy Algorithm
– Heap Active Inactive

– Active Object
– Active Live Object Inactive
Copy

Java Performance
27

Active Area

A C

B

R

Inactive Area

Java Performance
27

Active Area

A C
null null

B
null

R

Inactive Area

Java Performance
27

Active Area

A C
null

B
null

R
A’
null

Inactive Area

Java Performance
27

Active Area

A C
null

B

R
A’ B’
null null

Inactive Area

Java Performance
27

Active Area

A C

B

R
A’ B’ C’
null null null

Inactive Area

Java Performance
27

Inactive Area

R
A’ B’ C’
null null null

Active Area

Java Performance
28
Garbage Collection Algorithm artdb@ex-em.com | performeister.tistory.com


• Fragmentation
 Inactive Copy

• GC Suspend
• Copy Overhead
•

Java Performance
29

– Copying Algorithm
• Copy
• Object

•
Object
• Long Lived Object
– Heap age sub heap
Youngest Generation Sub heap GC
– Object Age

Java Performance
30

Youngest Generation Sub Heap

Matured Live Live Dead Dead

Live Matured Dead Live Dead

Dead Live Dead Dead Matured

Tenured Generation Sub Heap

Java Performance
30


Live Live Dead Dead

Live Dead Live Dead

Dead Live Dead Dead

Tenured Generation Sub Heap GC

Matured Matured Matured

Java Performance
30


Live Live

Live Live

Live

Tenured Generation Sub Heap GC


Java Performance
30


Matured Matured Dead
Live

Matured Dead

Live Matured Live

Tenured Generation Sub Heap


Java Performance
31
Garbage Collection Algorithm artdb@ex-em.com | performeister.tistory.com


• Sub Heap Mark-and-Sweep Copying Algorithm

Fragmentation, Memory , Copy

• JVM

Java Performance
32

• Train Algorithm
– Incremental Algorithm

– Memory
Mark-and-Copy GC

– GC Suspend
Idea

Java Performance
33

• Train Algorithm

Car : Memory Block , Fixed Size

RememberSet RememberSet
Car root
A B C A’ B’ C’ set

Train : Car( ) Car

Java Performance
34

Car 1-1 Car 1-2
Train 1 {R1,E}

A B C D E F

R1 Car 2-1
Train 2 {R2,B}
R2
G

Java Performance
34

Free Car Car 1-1 Car 1-2
Train 1 {C}

D E F C

R1 Car 2-1
Train 2 {R2,B}
R2
G

Car 3-1
Train 3 {R1}

A B

Java Performance
34

Free Car Free Car Free Car
Free Train

R1 Car 2-1
Train 2 {R2,B}
R2
G

Car 3-1
Train 3 {R1}

A B

Java Performance
35

• Train Algorithm

• Suspend

• Suspend
• Fragmentation

Java Performance
36

• Adaptive Algorithm
– Algorithm Trade Off
 Algorithm
– Adaptive Algorithm Algorithm

– Heap
Algorithm
– Hotspot Ergonomic , IBM Tilt

– Application

Java Performance

Hotspot JVM

Java Performance
38


Hotspot JVM Garbage Collection
1) Garbage Collection of Hotspot JVM
2) Heap of Hotspot JVM
3) Garbage Collector

4) Serial Collector
5) Incremental Collector
6) Parallel Collector
7) Parallel Compacting Collector
8) CMS Collector
9) Garbage First Collector

Java Performance
39
Hotspot JVM

• Garbage Collection of Hotspot JVM
– Weak Generational Hypothesis
• High Infant Mortality
• Few References from Older to Younger Objects
Exists
– Young Generation GC Algorithm
• Speed – Fast Allocation & TLAB
– Old Generation GC Algorithm
• – Card Table & Write Barrier

Java Performance
40
Hotspot JVM

• Fast Allocation & TLAB
T T T T T Synchronization
1 2 3 4 5 Wait
Allocation

T T T T T
1 2 3 4 5
TLAB Allocation Allocation Allocation Allocation Allocation

Java Performance
41
Hotspot JVM

• Fast Allocation & TLAB
– Memory
– Bump-the-Pointer
– Multi Thread
– Hotspot JVM TLAB
(Thread Local Allocation Buffer)
• Thread
• TLAB
• Allocation code
– 10 native instructions

Java Performance
42
Hotspot JVM

• Card Table Write Barrier
– 1 Byte Card / 512 Byte of Old Generation
– Old to Young Reference
– Write Barrier
• Bytecode Interpreter
• 2 native instructions
Young Generation

Old Generation

Card Table

Java Performance
43
Hotspot JVM

• Garbage Collection of Hotspot JVM
• Minor Collection : Young Generation
• Major Collection : Old Generation
– Full Collection
– Method Area GC Major Full

Java Performance
44
Hotspot JVM

• Heap of Hotspot JVM

Survivor 1

Survivor 2
Eden Tenured Permanent

Young Generation Old Generation Method Area

GC

Java Performance
45
Hotspot JVM

• JVM Option
– Standard Option
: JVM Option
:-
– Non-Standard Option
• JVM
• , Parameter
• -X Option : Macro
• -XX Option : Micro

Java Performance
46
Hotspot JVM

• Automatic Selection
– Java5 Garbage Collector,
Heap Size
– Hardware Resource OS
– Sever Class Client Class

Java Performance
47
Hotspot JVM

– Server Class
• :2 CPU, 2GB Physical Mem.
• 32bit Windows
• Default Garbage Collector Parallel Collector
• Initial Heap Size
– 1GB 1/64 * Physical Memory
– 1GB 32MB
• Max Heap Size : 1GB ¼ * Physical Mem.
• Server Runtime Compiler

Java Performance
48
Hotspot JVM

– Client Class
• Server Class
• Default Garbage Collector Serial Collector
• Initial Heap Size : 4MB
• Max Heap Size : 64MB
• Client Runtime Compiler

Java Performance
49
Hotspot JVM

– Option
• -server : Server Class
• -client : Client Class

Java Performance
50
Hotspot JVM

• Garbage Collector
– Serial Collector
• Hotspot JVM Default Garbage Collector
• Default Collector
• Young Generation : Generational Algorithm
• Old Generation : Mark-and-Compacting
Algorithm

Java Performance
51
Hotspot JVM

– Parallel Collector
• (Throughput) Garbage Collector
• Throughput Garbage Collector
• Young Generation
• Young Generation : Parallel Copy Algorithm
• Old Generation : Mark-and-Compacting
Algorithm

Java Performance
52
Hotspot JVM

– Parallel Compacting Collector
• Parallel Collector Old Generation

• Java SE 5.0 update 6
• Old Generation : Parallel Compacting
Algorithm

Java Performance
53
Hotspot JVM

– CMS Collector
• CMS : Concurrent Mark-Sweep
•
• Old Generation Pause Time
(Low Pause Garbage Collector)
• Old Generation : Concurrent Mark-and-
Sweep
Algorithm

Java Performance
54
Hotspot JVM

– Incremental Collector
• Low Pause Garbage Collector
• Train Collector
• Young Generation : Generational Algorithm
• Old Generation : Train Algorithm

Java Performance
55
Hotspot JVM

– Garbage First Collector
• Java SE 6 Update 14
• Train Algorithm
• Generation
• Heap Region
Young , Old Area
• Realtime Low Pause

Java Performance
56
Hotspot JVM

• Serial Collector
– Young, Old Generation Serial
(Single CPU Use)
– Suspend during Collecting
– Client Class Collector
–

Java Performance
57
Hotspot JVM

– Young Generation Collection :
Generational

Young Eden

A

Survivor1 - From Survivor2 - To

B C Empty

Old

Java Performance
57
Hotspot JVM

Generational
Minor GC
Young Eden

A


B C A’ B’ C’

Old

Java Performance
57
Hotspot JVM

Generational

Young Eden

Empty


Empty A’ B’ C’

Old

Java Performance
58
Hotspot JVM


Young Eden

A

Survivor1 - To Survivor2 - From

Empty B M

Old

Java Performance
58
Hotspot JVM


Minor GC
Young Eden

Empty

Survivor1 - To Survivor2 - From

A’ B’ Empty

Old
M’

Java Performance
59
Hotspot JVM

– Old Generation Collection
: Mark-and-Compacting

Old

Java Performance
59
Hotspot JVM


Mark

Old
√ √ √

Java Performance
59
Hotspot JVM


Sweep

Old
√ √ √

Java Performance
59
Hotspot JVM


Sliding Compaction

Old
√ √ √

Sliding Compaction : Fragmentation

Java Performance
60
Hotspot JVM

– JVM Option
• -XX:+UseSerialGC
: J2SE5.0, update 6 Serial Collector

• -XX:MaxTenuringThreshold=<value>
: Aging , default 31
• -XX:PretenureSizeThreshold=<value>
: Old Generation directly Allocation
• -XX:+PrintTenuringDistribution
: Promotion

Java Performance
61
Hotspot JVM

• Parallel Collector
– Memory, Multi-CPU

– GC Multi Thread
– Large Young Generation
– Server Class Default Garbage Collector
(CPU 1 )
: Serial Collector

Java Performance
62
Hotspot JVM

– Young Generation Collection : Parallel
Copy

Serial Collector Parallel Collector

Stop & Copy

Java Performance
63
Hotspot JVM

– Promotion Buffer
• Parallel Local Allocation Buffer(PLAB)
• Thread
• Promotion Thread Promotion
Buffer
• Fragmentation
– GC Thread
– Old Generation Size

Java Performance
64
Hotspot JVM

– Promotion Buffer

T1 T2 T1 T2

Promotion Buffer

Java Performance
65
Hotspot JVM

– Option
• -XX:+UseParallelGC : Parallel Collector
(CMS Collector )
• -XX:ParallelGCThreads=<value>
: GC Thread
default CPU

Java Performance
66
Hotspot JVM

– Ergonomics Option
• -XX:MaxGCPauseMills=<value>
(1.5+)
: Maximum Pause Time Goal
Pause Time
• -XX:GCTimeRatio=<value>
(1.5+)
: Throughput Goal , default 1%
GC Time
• -XX:+UseAdaptiveSizePolicy
(1.4.1+)
: Young/Old Sizing

Java Performance
67
Hotspot JVM

• -XX:YoungGenerationSizeIncrement=<value>
: Young Growing Percent, Default = 20
(1.5+)
•-
XX:TenuredGenerationSizeIncrement=<value>
: Old Growing Percent, Default = 20 (1.5+)
•-
XX:AdaptiveSizeDecrementScaleFactor=<value
>
: Growing Shrink , Default = 4 (1.5+)
• -XX:+AggressiveHeap
: Physical Memory Max Heap
Hardware Resource

Java Performance
68
Hotspot JVM

• -XX:GCHeapFreeLimit=<value>
(1.4.1+)
: GC Free Space
Heap (default 5)
-XX:+UseParallelGC GC
OOME
• -XX:GCTimeLimit=<value>
(1.4.1+)
: GC
(default 90)
-XX:+UseParallelGC GC
OOME

Java Performance
69
Hotspot JVM

• Parallel Compacting Collector
– Parallel Collector Old Generation
Collection Algorithm
– Parallel Collector
– Multi CPU
– Young Generation Collection
• Parallel Copy Algorithm

Java Performance
70
Hotspot JVM

: Parallel Compaction

Parallel Compacting Collector

Mark Phase

Summary Phase

Compaction Phase

Java Performance
71
Hotspot JVM

– Mark Phase
• Generation Region
• Live Object Marking
• Parallel Work

Java Performance
71
Hotspot JVM

– Mark Phase
• Generation Region
• Live Object Marking
• Parallel Work

      

Java Performance
72
Hotspot JVM

– Summary Phase
• Region Operation
• Single Work
• Density
• Dense Preﬁx
• Dense Preﬁx GC

      

Java Performance
72
Hotspot JVM

– Summary Phase
• Region Operation
• Single Work
• Density
• Dense Prefix
• Dense Prefix GC

      

Dense Prefix

Java Performance
73
Hotspot JVM

– Compaction Phase
• Thread Region Collecting
• Source, Destination
• Live Object Destination
Compaction

      

Java Performance
73
Hotspot JVM

Compaction

Destination Source

      

Java Performance
73
Hotspot JVM

Compaction

Destination Source

      

T1 T2

Java Performance
73
Hotspot JVM

Compaction

Destination Source

      

T1

Java Performance
74
Hotspot JVM

– Option
• -XX:+UseParallelOldGC (+Java6)
: Parallel Compaction Collector
• -XX:+UseParallelOldGCCompacting
(+Java6)
: Parallel Compaction , Default True
• -XX:+UseParallelDensePreﬁxUpdate
(+Java6)
: Dense Preﬁx , Default True

Java Performance
75
Hotspot JVM

• CMS Collector
– Fast Elapsed Time
– Old
Generation
– Low Latency Collector
–
– GC Pause Time

– Young Generation Collection

Java Performance
76
Hotspot JVM

• CMS Collector
: Concurrent Mark-Sweep
Concurrent Mark-Sweep Collector

Java Performance
76
Hotspot JVM

• CMS Collector

Initial Mark Phase

Java Performance
76
Hotspot JVM

• CMS Collector

Initial Mark Phase

Concurrent Mark Phase

Java Performance
76
Hotspot JVM

• CMS Collector

Initial Mark Phase


Remark Phase

Java Performance
76
Hotspot JVM

• CMS Collector

Initial Mark Phase


Remark Phase
Concurrent Sweep Phase

Java Performance
77
Hotspot JVM

• CMS Collector
• Initial Mark Phase
– Serial Phase
– Direct Referenced Object
• Concurrent Mark Phase
– Serial Phase
– Application
– Direct Reference Object

Java Performance
78
Hotspot JVM

• CMS Collector
• Remark Phase
– Parallel Phase
– Marking Mark
• Concurrent Sweep Phase
– Serial Phase
– Dead Object Reclaim
– Compaction

Java Performance
79
Hotspot JVM

• CMS Collector
– No Compaction!!!
• , But Free Space
 FreeList
• Fast Allocation
: Promotion Young

    

Java Performance
79
Hotspot JVM

• CMS Collector
– No Compaction!!!
• , But Free Space
 FreeList
• Fast Allocation
: Promotion Young

Java Performance
80
Hotspot JVM

• CMS Collector
• Fragmentation
 Object Size Tracking,

 Free Block

Java Performance
81
Hotspot JVM

• CMS Collector
– Concurrent Mark Allocation

– Floating Garbage
• Concurrent Mark Garbage
• Next GC
• Memory

Java Performance
82
Hotspot JVM

• CMS Collector
– Floating Garbage

Java Performance
83
Hotspot JVM

• CMS Collector
– Scheduling Collection
• Old Generation Full
• Old Generation Full
GC
• Minor GC Remark
Minor GC
• Current Heap

• : Heap 68%

Java Performance
84
Hotspot JVM

• CMS Collector
– Option
• -XX:+UseConcMarkSweepGC
(1.4.0+)
: CMS Collector
(+XX:UseParallelGC )
• -XX:+UseParNewGC (1.4.1+)
: Young Parallel Option
• -XX:CMSInitiatingOccupancyFraction
(1.4.1+)
: Current Old Generation

Java Performance
85
Hotspot JVM

• CMS Collector
– Incremental Mode
• Concurrent phase
• Concurrent Phase

Java Performance
85
Hotspot JVM

• CMS Collector

Initial Mark Phase

Java Performance
85
Hotspot JVM

• CMS Collector

Initial Mark Phase


Remark Phase

Java Performance
85
Hotspot JVM

• CMS Collector

Initial Mark Phase
CPU
Concurrent Mark Phase GC

Remark Phase

Java Performance
86
Hotspot JVM

• CMS Collector
• Minor GC Concurrent Phase

• Duty Cycle Concurrent Collector

• Duty Cycle
–1 CPU
– Minor GC
– I-CMS ( ) or

Java Performance
87
Hotspot JVM

• CMS Collector
– Option
• -XX:+CMSIncrementalMode (1.4.2+)
: Incremental Mode (default False)
CMS
CMSInitiatingOccpancyFraction
• -XX:+CMSIncrementalPacing (1.4.2+)
: Duty Cycle (default False)

Java Performance
88
Hotspot JVM

• CMS Collector
• -XX:CMSIncrementalDutyCycle=<value>
(1.4.2+)
: Duty Cycle (default 50)
Minor GC (0~100)
50
• -XX:CMSIncrementalDutyCycleMin=<value>
: Duty Cycle (0~100)
(Default 10) (1.4.2+)

Java Performance
89
Hotspot JVM

• CMS Collector
•-
XX:CMSIncrementalSafetyFactor=<value>(1.4.2
+)
: Duty Cycle
(Default 10)
• -XX:CMSIncrementalOffset=<value>
(1.4.2+)
: Duty Cycle Minor GC
(0~100) (Default 0)

Java Performance
90
Hotspot JVM

• CMS Collector
• -XX:CMSExpAvgFactor=<value>
(1.4.2+)
: %
(Default 25) (0~100)

Java Performance
91
Hotspot JVM

• Incremental Collector
– Train Collector
– Old Generation Pause Time
– Young Generation Collection : Stop-the-
Copy
– Old Generation Collection : Train
• Old small GC
• OOME Mark-and-Compaction

– Old Fragmentation

Java Performance
92
Hotspot JVM


Java Performance
93
Hotspot JVM

– Minor GC
• Minor GC Major GC (overhead)
• Minor GC Old GC
• Throughput Default collector

• Pause Time

Java Performance
94
Hotspot JVM

– Collector
– Option
• -Xincgc : Incremental GC
: -XX:+UseParallelGC, -XX:+UseParNewGC

Java Performance
95
Hotspot JVM


Garbage Young Generation Old Generation
Option
Collector Collection Algorithm Collection Algorithm

Serial Collector -XX:+UseSerialGC Generational Mark-and-Compacting
(Default Collector)

Parallel Collector -XX:+UseParallelGC Parallel Copy Mark-and-Compacting

Parallel
Compacting -XX:+UseParallelOldGC Parallel Copy Parallel Compacting
Collector
-XX: Concurrent
CMS Collector +UseConcMarkSweepG Parallel Copy
C Mark-Sweep
Incremental
-Xincgc Generational Train
Collector

Java Performance
96
Hotspot JVM

• Option
• -XX:+DisableExplicitGC
: System.gc()
• -XX:+PrintGC
• -XX:+PrintGCDetails
• -XX:+PrintGCTimeStamps
• -XX:+PrintHeapAtGC
• -Xloggc:<ﬁle>
• -verbosegc

Java Performance
97
Hotspot JVM

• Garbage First Collector
– Java SE 6 update 14
– Realtime
• Y ms interval x ms GC
– Single Generation
• Generation
• Heap region
– 1MB Best Region
• Young Generation : a Set of Regions
– Allocation Region Young Generation
• Old Generation : a Set of Regions

Java Performance
98
Hotspot JVM

– Garbage First
• Concurrent Marker Heap Region live
data
• Live Data Garbage Region
• Garbage Region

Java Performance
99
Hotspot JVM

– Garbage First Collection

Java Performance
99
Hotspot JVM


Young GC (Evacuation Pause)

Java Performance
99
Hotspot JVM



Concurrent Mark - Marking

Java Performance
99
Hotspot JVM




Concurrent Mark - Remarking

Java Performance
99
Hotspot JVM





Old Region Reclaim - Remark

Java Performance
99
Hotspot JVM






Old Region Reclaim – Evacuation Pause

Java Performance
99
Hotspot JVM






Old Region Reclaim – Evacuation Pause

Compaction

Java Performance
100
Hotspot JVM

• Young GC (Evacuation Pause)
– Live Object Survivor
Region Old Region

– Stop-the-Copy
– Parallel

Java Performance
101
Hotspot JVM

• Concurrent Marking
– Mark : Evacuation Pause Initial Mark
– Remark : Region Live
Empty Region reclaim
Stop the World

Java Performance
102
Hotspot JVM

• Reclaim Old Region
– Live Object Region
– old Region collected

Java Performance
103
Hotspot JVM

• Compaction
– Large chunk Free Space
– Fragmentation
– Fast Allocation
» Free List
» Linear
» TLAB
– - Copy Pause Time

Java Performance
104
Hotspot JVM

– Options
• -XX:+UnlockExperimentalVMOptions
• -XX:+UseG1GC

Java Performance

IBM JVM

Java Performance
106


IBM JVM Garbage Collection
1) Heap of IBM JVM
2) Heap Expansion Shrink

3) Garbage Collector

4) Optimize for Throughput

5) Optimize for Pause Time
6) Generation Concurrent
7) Subpooling

Java Performance
107
IBM JVM

• Heap Layout
– 1.4 Heap
– Single Space

heapbase heaplimit heaptop
• Heap
• Heapbase : Heap
• Heaplimit : (movable)
• Heaptop : Heap

Java Performance
108
IBM JVM

• Heap Layout
– 1.4 Heap

heapbase heaplimit heaptop

Heap
K Cluster

P Cluster

Wilderness
Heap cache or
LOA

Java Performance
109
IBM JVM

• Heap Layout
• Kcluster : Pinned Class Object
– Default 1280 class entries
– 1 Class Entry 300byte(32it), 560byte(64bit)
• Pcluster : Pinned Object
• Kcluster Pcluster
• Pcluster 2KB Pcluster
• Pcluster

Java Performance
110
IBM JVM

• Heap Layout
– Large Object Area
• Large Object
• 64KB Object
• Heap
• -Xloratio LOA
(0.5 ~ 0.95 )
• Java5 -Xloainitial (default 0.05, 5%), -
Xloamaximum(default 0.5, 50%)
• 1MB Object

Java Performance
111
IBM JVM

• Heap Layout
Garbage Object Live Object

Java Performance
112
IBM JVM

• Heap Layout - Subpool
– Free Chunk FreeList
– -Xgcpolicy: subpool
– Pool FreeList, CPU

Pool

1 Small Size Freelist Middle Size Freelist

2
3
4
5
…

Large Size Freelist
n

Java Performance
113
IBM JVM

• Heap Layout
– Java 5 Heap
– Heap Generational Heap
– -Xgcpolicy: gencon

Allocation Space Survivor Space Tenured Space

Nursery Tenured

Java Performance
114
IBM JVM

• Heap Allocation
– Heap Lock
• 512byte Object
• Heap Lock Free List
• GC
• Free Chunk Heap Lock
– Dark Matter
• Free Chunk 512
byte Freelist
• Dark Matter compaction

Java Performance
115
IBM JVM

• IBM JVM Heap
– Heap Options
• -Xmx<value> , -Xms<value>
• -Xmaxf<percentage>
: Free Space (default 0.6, 60%)
• -Xminf<percentage>
• -Xloa :loa , subpool default
• -Xmaxe<size> heap expansion (default
0)

Java Performance
116
IBM JVM

• IBM JVM Heap
– Heap Options
• -Xk<classes> (~1.4.2)
– Kcluster
– class
– Class 1.1~1.15

• -Xp<initial>,<overﬂow>
(~1.4.2)
– Pcluster
– initial Size OverFlow

Java Performance
117
IBM JVM

• Heap Expansion Shrink
– Expansion
• Expansion
· Garbage Collector Allocation

· Free Space –Xminf
· GC –Xmaxt

Java Performance
118
IBM JVM

– Expansion
• Expansion
· Free Space -Xmaxf –Xmaxf
· –Xmaxe –Xmaxe
· –Xmine –Xmine
· Expansion 32bit 512byte
64bit 1024byte

Java Performance
119
IBM JVM

– Shrink
• Shrink
· Garbage Collection

· -Xmaxf 100%
· System.gc() free space –Xminf
· Heap 3 GC
• free space –Xmaxf
Shrink

Java Performance
120
IBM JVM

– Shrink
• Shrink
– -Xmaxf –Xms
– 32bit 512byte 64bit 1024byte

Java Performance
121
IBM JVM

• IBM JVM Heap
– Heap Size Options
• -Xmaxf<percentage>
• -Xminf<percentage>
• -Xmaxe<size> heap expansion (default
0)
• -Xmine<size> heap expansion (default
1MB)
• -Xmaxt<percentage>

Java Performance
122
IBM JVM

• IBM JVM Heap
– Garbage Collection Options
• -Xgcpolicy:<optthruput | optavgpause | gencon
| subpool>
: Garbage Collector
• -Xdisableexplicitgc
: System.gc()
• -Xverbosegclog:<path to file>[X,Y]
: file gc log
: X,Y integer X file , Y GC Cycle
• -verbose:gc : gc

Java Performance
123
IBM JVM

• IBM JVM Heap
• -Xcompactexplicitgc
– System.gc() Compaction (default)
• -Xnocompactexplicitgc
– System.gc() Compaction
• -Xcompactgc
– GC Compaction (default)
• -Xnocompacgc
– GC Compaction

Java Performance
124
IBM JVM

• IBM JVM Heap
• -Xcompactexplicitgc
– System.gc() Compaction (default)
• -Xnocompactexplicitgc
– System.gc() Compaction
• -Xcompactgc
– GC Compaction (default)
• -Xnocompacgc
– GC Compaction

Java Performance
125
IBM JVM

• IBM JVM Garbage Collector
– -Xgcpolicy
– Optimize for throughput (optthruput)
• Default garbage collector
•
– Optimize for pause time (optavgpause)
• Concurrent GC
• GC pause time
•

Java Performance
126
IBM JVM

• IBM JVM Garbage Collector
– Generational Concurrent (gencon)
• Object
• Generational Heap
– Subpooling (subpool)
• Default algorithm
• 16 CPU SMP

Java Performance
127
IBM JVM

• Collector Algorithm
Mark Phase Sweep Phase Compaction Phase

1.4 - Incremental
optthruput Parallel Mark Parallel bitwise Sweep Compaction,
5.0–Parallel Compaction

1.4-Parallel bitwise 1.4 - Incremental
Sweep, Compaction,
optavgpause Concurrent Mark
5.0-Concurrent 5.0-Mostly Concurrent
Sweep Compaction
Scavenge Copy of New Area
Global Collection of Old Area
gencon
Mostly Concurrent
Concurrent Mark Parallel bitwise Sweep
Compaction
1.4 - Incremental
subpool Parallel Mark Parallel bitwise Sweep Compaction,
5.0–Parallel Compaction

Java Performance
128
IBM JVM

• Optimize for throughput
– Application
– Default Garbage Collector
– Parallel Algorithm
– GC Application Suspend
– Mark-Sweep phase GC Cycle

– Compaction Fragmentation AF

• Allocation Failure(AF) :

Java Performance
129
IBM JVM

– Mark-Sweep & Compaction

Java Performance
129
IBM JVM

– Mark-Sweep & Compaction

Mark Phase

 

Java Performance
130

IBM JVM

– GC Thread

Java Performance
130

IBM JVM

– GC Thread

Mark

Java Performance
130

IBM JVM

– GC Thread

Mark

Sweep

Java Performance
130

IBM JVM

– GC Thread

Mark

Sweep

Compaction

Java Performance
131

IBM JVM

– Mark Phase : Parallel Mark
• 1.4 : Mark Stack
• Java 5 : Work Packet
– Sweep Phase : Parallel Bitwise Sweep
• 1.4 : Incremental Compaction
• Java 5 : Parallel Compaction

Java Performance
132
IBM JVM artdb@ex-em.com | performeister.tistory.com

• Tracing Live Object Mark
• Live Object
– Register, stack, static, jni Object
– Move dosed bit on
– Mark bit
– Mark Stack
– Mptr class object mark
– Array array entry trace

Java Performance
133

• Mark Stack (1.4)
– Trace Live Object reference
– Marking Thread 4KB Mark Stack
– Marking Thread thread Stack scan
reference push, mark bit
– Garbage Collector Pop
Object Mark
– Array Array Entry Mark
– MSO(Mark Stack Overﬂow)
» Object NotYetScanned bit Global Flag
» Object
» Thread
» Heap

Java Performance
134

• Work Packet(5.0)
– Java5 Work Packet Pool
– Work Packet Mark Stack
– Marking Thread 2 Work Packet
» Input Packet : reference pop
» Output Packet : Unmarked Object Push
» Reference Output Packet Push Mark

Java Performance
135

• Work Packet(5.0)
– Root Object mark bit
reference output packet
– Root Object Reference input Packet
Pop Object
– List

Java Performance
136

• Parallel Mark(1.4)
– Mark
– application Thread master gc thread
helper thread
– Helper Thread 4KB Mark Stack Shareable
Queue 2KB Mark Queue
• Parallel Mark(5.0)
– helper Thread Work Packet Pool

Java Performance
137

• Alloc bits Mark Bits Reference
Allocated Object
• Bit Wised Technique
– Mark bits 0 Free Space
– 512 byte freelist
• Sweep mark bits alloc bits

Java Performance
138
IBM JVM

Garbage Object Live Object

Java Performance
139

• Parallel Bit-wised Sweep
– Sweep
– Heap N Section
» 1.4 : N Helper Thread *32, heap size / 16MB

» 5.0 : N heap size / 256KB, 256KB ﬁxed
Size
– Helper Thread Section Scan & Sweep
– Section Free List

Java Performance
140

IBM JVM

• Compaction
– GC
– Sweep Allocation Request

– System.gc() AF Compaction

– TLH
TLH 1000Byte(1.4) 1024Byte(5.0)
– Free Space Active heap 5% 128MB

Java Performance
141

• 1.4 Compaction
– Unmovable Object
– Incremental Compaction Algorithm

• 5.0 Compaction
– Parallel Compaction
– Unmovable Object

Java Performance
142

IBM JVM

• Incremental Compaction(1.4)
– Compaction Compaction
– 128MB Heap
– Heap Section Section Compaction
– 1.4.2 Default
– Mark Phase Section Free Space
– Object , , Pointer
– Section GC

Java Performance
143

– UnMovable Object (~1.4.2)
• Dosed Object
– Stack(Local Variable, Method Parameter)
Object
– Dosed bit on,
• Pinned Object
– JNI, Class Object, Other Pinned Object
– Pinned bit On,

Java Performance
144

IBM JVM

– UnMovable Object

pinned
dosed
Compaction

pinned
dosed

Java Performance
145

IBM JVM

• Incremental Compaction(1.4)

Dark Matter

One Section per Thread

Java Performance
146

IBM JVM

• Parallel Compaction(1.5)
– Heap n area
– Area Heap Size CPU, thread

– Thread Area Compaction
–
» Move Step : Object
» Fix-up Step : Object Reference

Java Performance
147

IBM JVM

– Move Step

T1 T2

T1 T2

Java Performance
148

IBM JVM

– Move Step
» Thread Source Area Destination Area
» Object Moving Pointer bitmap
» Hole Area

» Area Size Hole Load
Balancing

Java Performance
149

IBM JVM

– Fix-up Step
» reference update
» Block table
» Block 256Kb Heap
» Fix-up Block
» Block object ,
» Object Block

Java Performance
150

IBM JVM

– Block Table
» Block 1 Pointer
» Block Object
– Object Bitmap
» Old Bitmap : Move Object (Mark Phase)
» New Bitmap : Move Object (Moving Step)

Java Performance
151

IBM JVM

– Options
• -Xgcthreads<thread >
– GC Parallel Thread
– Default CPU – 1, Min 1, Max CPU
• -Xgcworkpackets<numbers>
– Workpacket default maximum heap size
packet
• -Xpartialcompactgc
– Incremental compaction (1.4.2 default)
– 5.0 not set, full compaction
• -Xnopartialcompactgc
– Incremental Compaction

Java Performance
152

IBM JVM

• Optimize for pause time
– GC Pause Time
– Background thread Application
concurrent mark, sweep
– Mark Phase : Concurrent Mark
– Sweep Phase
• 1.4 -Parallel bitwise Sweep,
• Java 5 -Concurrent Sweep
• 1.4 - Incremental Compaction,
• Java 5 -Mostly Concurrent Compaction

Java Performance
153

IBM JVM

~ 1.4.2 Java5 ~

Java Performance
153

IBM JVM

~ 1.4.2 Java5 ~

Concurrent Mark

Java Performance
153

IBM JVM

~ 1.4.2 Java5 ~

Concurrent Mark

Sweep

Java Performance
153

IBM JVM

~ 1.4.2 Java5 ~

Concurrent Mark

Sweep

Compaction

Java Performance
153

IBM JVM

~ 1.4.2 Java5 ~

Concurrent Mark Concurrent Mark

Sweep

Compaction

Java Performance
153

IBM JVM

~ 1.4.2 Java5 ~


Sweep Concurrent Sweep

Compaction

Java Performance
153

IBM JVM

~ 1.4.2 Java5 ~


Sweep Concurrent Sweep

Compaction Compaction

Java Performance
154

IBM JVM

– Concurrent Mark
• Thread Stack Scan
root
• Trace background thread
• Thread marking
– trace Object
– Object reference write barrier
heap
– Heap 512byte 1byte card card
table
– Reference object
0x01

Java Performance
155

– Concurrent Mark
• Object Allocation ‘tax’ rate
– STW
– heap Marking
– Garbage Collection Thread Application Thread

Tax

Java Performance
156

IBM JVM

– Stop the World Phase
• Root Scan
• Marked Card
• Sweep
• Floating Garbage

Java Performance
157

IBM JVM

– Concurrent Sweep Phase
• Java 5
• 1.4.2 Parallel Bitwise Sweep Algorithm

• Parallel bit-wise Sweep
• Heap Section Allocation
Sweep
•
– Sweep Analysis
» Markbit Data Section
» Freelist
– Connection

Java Performance
158

IBM JVM

– Concurrent Sweep Phase
• Heap Section parallel bitwise sweep

• Sweep STW
• Allocation Process Concurrent Sweep

• Compaction
• Mark .

Java Performance
159

IBM JVM

– Mostly Concurrent Compaction
• Java 5
• 1.4 Incremental Compaction
• Compaction
• STW Partial Move
– Sweep Compact
• Fixup Concurrently
– Compaction Pause Time

Java Performance
160

IBM JVM

• Move Step
– Application
» Map2 Heap Fixup view
» Map2 : Virtual Address range
Physical Memory Map
– Compact Area
» Sweep Object Layout
Compaction Section
– Move – Object Compaction

Java Performance
161

IBM JVM

• STW Fix-up
– Root Reference Fixup
– Heap page
» Object Heap Page
» Object Heap Page Unﬁxed
– Lock
» Free Page Fixed
– Application Thread

Java Performance
162

IBM JVM

• Concurrent Fix-up
– unfixed page fixed
– Unfixed(protected)  Busy  Fixed(unprotected)
– Application fixed Page
– Exclusive Fixer : Fix Thread
– Collector Thread Fix
– Trapped Thread : Application Thread Unfixed page
Trap Routine

Java Performance
163

IBM JVM


Unfixed

Unfixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Collector Unfixed

Unfixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Exclusive
Collector Unfixed
Fixer

Unfixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Exclusive
Collector Unfixed
Busy
Fixer

Unfixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Exclusive
Collector Unfixed
Fixed
Busy
Fixer

Unfixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Collector Unfixed
Fixed
Busy

Unfixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Exclusive
Collector
Fixer Unfixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Exclusive
Collector
Fixer Unfixed
Busy

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Exclusive
Collector
Fixer Unfixed
Busy
Fixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Mutator Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

blocke
Mutator d Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Trapped
Mutator Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Exclusive
Trapped
Mutator
Fixer Unfixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Exclusive
Trapped
Mutator
Fixer Unfixed
Busy

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Exclusive
Trapped
Mutator
Fixer Unfixed
Busy
Fixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Trapped
Mutator Unfixed
Busy
Fixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Mutator Unfixed
Busy
Fixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Mutator
Unfixed
Busy
Fixed

Unfixed

Java Performance
163

IBM JVM


Unfixed
Fixed
Busy

Collector Unfixed
Busy
Fixed

Unfixed

Unfixed
Busy
Fixed

Unfixed

Java Performance
164

IBM JVM

– Options
• -Xconcurrentbackground<number>
– Concurrent mark background GC
Application Thread
– Default 1
• -Xconcurrentlevel<number>
– Tax rate
– heap Tax
– Default 8

Java Performance
165

IBM JVM

– Options
• -Xconmeter:<soa:loa:dynamic>
– Concurrent Mark Allocation Tax
– Dynamic
– Default soa (Small Object Area)

Java Performance
166

IBM JVM

• Generation concurrent
– Generation Heap

Allocation Space Survivor Space Tenured Space

New Area (Nursery) Old Area

Java Performance
167

IBM JVM

– Nursery : Object
• Allocate Space : Object
• Survivor Space
: Allocate Space Allocation Failure
Scavenge-Copy (GC : Stop-the-Copy)
: Live Object
• Allocate Space Survivor Space Flip

Java Performance
168

IBM JVM

– Tenured : Object Promotion
• 14 GC Aging Promotion (adaptive)
• Optavgpause concurrent mark
• But sweep concurrent
– Tilt Ratio : Adaptive

Survivor
Allocation Space Survivor Space Allocation Space
Space

50% 80%

Java Performance
169

IBM JVM


Java Performance
169

IBM JVM


Scavenge Copy

Concurrent Mark

Java Performance
169

IBM JVM


Scavenge Copy

Concurrent Mark

Scavenge Copy

Concurrent Mark

Java Performance
169

IBM JVM


Scavenge Copy

Concurrent Mark

Scavenge Copy

Concurrent Mark

Global Collection

Java Performance
169

IBM JVM


Scavenge Copy

Concurrent Mark

Scavenge Copy

Concurrent Mark

Global Collection

Scavenge Copy

Java Performance
170

IBM JVM

– Scavenge GC
• New Area Garbage Collection
• Stop The Copy Algorithm
– Global GC
• Tenured Area optavgpause Concurrent
Mark
• Concurrent Sweep
• Nursery, tenured
• GC Application Suspend
• Compaction

Java Performance
171

IBM JVM

– Options
• -Xmn<size>
– New Area
• -Xmns<size> : New Area
• -Xmnx<size> : New Area
• -Xmo<size>
– Old Area
• -Xmos<size> : Old Area
• -Xmox<size> : Old Area

Java Performance
172

IBM JVM

• Subpooling
– 16 CPU
– Size Heap
• Pool freelist
• Pool sorting
• Fast allocation
– Allocation Heap Lock

• CPU Pool

Java Performance
173

IBM JVM

• Subpooling
– Subpool
• JVM Compaction
Subpool
• GC Sweep phase subpool
• Concurrent Algorithm

Java Performance
174

3장. Garbage Collection

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